1. Field of the Invention
This invention relates to combination gas bearing and seal apparatus and more particularly to such combination type apparatus of the rotary type.
2. Description of the Prior Art
Combination rotary gas bearing and sealing devices are well known in the art, cf. for example, U.S. Pat. Nos. 2,814,512, 3,733,490, 4,118,042, 4,191,385, and 4,361,332, to name just a few. In general, in such devices the gas of the bearing is used to effect the seal. However, heretofore in the prior art of which I am aware, the seal could only seal off a region of the bearing which encompassed the axis of rotation of the bearing, the seal and region being generally concentric with the axis. Thus, the prior art devices were not amenable to system apparatus in which there is a need to provide a seal for a region between two planar gas bearing surfaces of the bearing that is offset from the axis of rotation, i.e. a region which is radially offset from and doesn't include the axis of rotation, such as, for example, as is required in the entry system apparatus of my aforementioned copending application. Hence, the prior art devices were not amenable to providing a seal for a low pressure region, e.g. a vacuumized opening, in a rotary gas bearing using air or the like where the region has to be radially offset from and not encompass the bearing's axis of rotation.
In the automatic filling machine of U.S. Pat. No. 4,205,711, which is used for the dosing of powder from a hopper through an intermediate sector body to a rotatable dosing head, compressed air is used in the spacing between the concentric curved surfaces of the dosing drum head and the sector body to provide a hermetic seal for the opening of the body and the underlying powder carrying chambers of the rotating drum head. The hermetic seal provided by the compressed air is only operative when the head is rotating, and, moreover, only during the rotation is the hermetic seal intended to prevent the powder from the opening of the body from entering the opening of the carrying chamber. During the rotational movement periods of the drum head, the sector body is in a retracted outward radial position with respect to the rotating head and is maintained at a spacing with respect to the head by a set of locator pins. During the periods of non-rotation of the head, the sector body is in an extended radially inward position that places the body in contact with the head via another set of locator pins. The compressed air is and must not be present during these last mentioned periods so as to allow the transfer, which is in the radial direction, of the powder from the opening of the body to the aligned opening of one of the plural powder carrying chambers by suction means, which gas if otherwise present would prevent the transfer as explained previously. Thus, even though the compressed gas may also provide some lubrication between the moving parts, it is and can only be present during the actual rotation periods. Because of the intermittent presence of the gas and/or because of the requirement of curved surfaces for the sealing and/or lubrication operation, this prior art system is only useful for passing the powder through the aligned openings in a radial direction. In addition, the spacing between the two surfaces are maintained exclusively by independent mechanical means. Due to variations in the concentricity of the respective surfaces such as, for example, misalignment with respect to the axis of rotation, the seal is subject to leakage. Thus, this prior art system is not very reliable and/or has poor throughput rates. Moreover, it is particularly not conducive for vacuum to vacuum entry systems and/or particularly for vacuum to vacuum entry systems of the rotary type in which the article passes through in a direction parallel to the axis and/or where the seal is required to be present as the transferring of the article from one vacuum to the other vacuum is taking place.